GM-GMC: 98 chevy silverado 350, torque convertor, chevy silverado

Question
The truck run well. It has 170K on it. The problem which is not real bad but concerning is that when driving done the highway, the RPM's raise and lower about a 1000. I only got the truck a few weeks ago. Thanks Ted

Answer
If you don't notice any other performance problems engine wise, I would guess you have a transmission problem.  It is possible that the torque convertor is locking and unlocking on the hiway causing the change in rpm.  I am not a tranny specialist by any means, but what you could try would be to try it in drive not overdrive and see if the problem persists.  Aside from that you may need to take a tranny guy for a ride and get their opinion.
Hope this helps.